The present invention relates to a hearing aid for arrangement in the ear, particularly completely inside the ear canal, comprising a plug for arrangement in the ear canal and having a shell-like wall facing the interior of the ear canal and an outward faceplate which together define a generally closed cavity in which are arranged an input transducer, such as a microphone, for transforming external sounds into an electrical signal, a signal processor for processing the signal produced by the input transducer and producing a hearing-loss compensating electrical signal, and an output transducer for transforming the signal from the signal processor into a hearing-loss compensating sound signal, as well as a power source, such as a battery.
In hearing aids of this type, so-called occlusion effects often occur during use as a consequence of the closure of the ear canal caused by the hearing aid, which occlusion effects manifest themselves by the user experiencing his or her voice as dominant, because voice sounds are transmitted through bones and tissue to the residual volume which is located innermost in the ear canal and is defined by the housing of the hearing aid and the eardrum. Furthermore, changes in the differential pressure between the air in this confined volume and the atmosphere, for example when the user is inside an ascending airplane, may give rise to an unpleasant feeling, which can usually, however, be counteracted by the user making jaw movements that propagate to the ear canal and create pressure-equalizing leakages between the ear canal wall and the hearing aid.
To solve this problem it is well-known to provide both hearing aids of the type stated and ear plugs for conventional behind-the-ear hearing aids with a through-going vent passage from the innermost end of the hearing aid or the ear plug to the surroundings. Typically, such a vent passage or vent is formed as a hose or a tube extending through the hearing aid plug. However, this measure is disadvantageous in that it often gives rise to acoustical feedback because part of the sound amplified by the hearing aid and produced in the ear canal reaches the microphone of the hearing aid.
Some ear plugs without an integral hearing aid have a cavity in the vent passage to remedy this problem. The purpose of this design is to make the vent passage with such intermediate cavity act like a low-pass filter to damp the passage of high-frequency sounds and thus reduce the tendency of acoustical feedback.
Solutions of this type are described, i.a., in the following articles by John Macrae:
xe2x80x9cA new kind of earmold vent the high-cut cavity ventxe2x80x9d, Hearing Instruments, vol. 32, No. 10, 1981, page 18 pp.,
xe2x80x9cAn improved version of the high-cut cavity ventxe2x80x9d, Australian Journal of Audiology, 1981 3:2, pages 36-39,
xe2x80x9cVenting without feedbackxe2x80x94further development of the high-cut cavity ventxe2x80x9d, Hearing Instruments, vol. 33, No. 4, 1982, page 12 pp., and
xe2x80x9cA damped high-cut cavity vent for profound hearing lossxe2x80x9d, Australian Journal of Audiology, 1982 4:1, pages 22-25.
The vent systems discussed here for ear plugs function as ordinary vent passages as well as acoustic low-pass filters.
For hearing aids of the type indicated above of the ITE design, corresponding vent systems are known from, i.a., CH-A-681,125, the cavity coupled in here being constituted by the part of the cavity in the hearing aid housing not taken up by electronic components.
U.S. Pat. No. 5,195,139 further describes a hearing aid in which, from a conventional vent passage formed by a longitudinal canal through the wall or shell of the hearing aid plug, an opening has been established into a closed cavity in the hearing aid. The system functions as a Helmholtz resonator, whereby transmission of undesired frequencies through the vent passage is damped. This is high-frequency damping in the range from 2.0 to 6.5 kHz. In addition to this filter characteristic, the vent passage functions as an ordinary vent passage.
Accordingly, it is an object of the invention to provide a hearing aid of the type stated, in which a significant damping of occlusion effects can be obtained without the use of a conventional vent passage or vent with the consequent problems in the form of manufacturing and mounting complications, acoustical feedback, etc.
For a hearing aid of the type stated, this is obtained according to the invention in that an acoustical link in the form of a hose or tube piece is provided between an orifice at the external side of the part of the wall of the plug facing the interior of the ear canal and the residual volume of the internal cavity of the plug and, together with said residual volume in the cavity, forms an approximated acoustical circuit having a resonance frequency in the region of the first voice sound formants of the user.
By means of the invention, undesired occlusion effects are damped through the increase of the residual volume constituted by the part of the cavity in the hearing aid housing which is not taken up by the electronic components of the hearing aid and produced by said acoustical link in the interior of the ear canal within the hearing aid, and this increase of volume is made virtually larger at the resonance frequency of the acoustical circuit. Through the increase of the residual volume, the sound pressure of occlusion sounds is reduced, since the surfaces that transmit the occlusion sounds are not changed. Thereby the invention can damp occlusion sounds both with and without a through-going vent passage, as explained in detail below.
Formation of said approximated acoustical circuit having a resonance frequency in the region of the first voice sound formants of the user, typically in the region from about 200 to about 800 Hz, causes a damping of the otherwise bothering propagation of the user""s voice sounds.
According to one embodiment of the invention, a certain softening of this damping may be obtained, if desired, by a through-going vent passage or vent being provided as well from said residual volume in the ear canal to the surroundings.
The invention also relates to a method for the production and user-fitting of a hearing aid of the type stated, whereby a plug formed for arrangement in the ear canal is manufactured with a substantially closed shell-like wall facing the interior of the ear canal and an outward faceplate which together define a generally closed cavity in which are arranged an input transducer, such as a microphone for transforming external sound into an electrical signal, a signal processor for processing the signal produced by the input transducer and producing a hearing-loss compensating electrical signal, and an output transducer for transforming the signal from the signal processor into a hearing-loss compensating sound signal, as well as a power source, such as a battery.
According to the invention, this method is characterized in that an acoustical link in the form of a hose or tube pice is provided between an orifice at the external side of the part of the wall of the plug facing the interior of the ear canal and the residual volume of the internal cavity of the plug, which hose or tube piece is tuned so that together with said residual volume in the cavity it forms an approximated acoustical circuit having a resonance frequency in the region of the first voice sound formants of the user.
Thereby the occlusion-effect-reducing acoustical link can be provided in a simple manner in a completed hearing aid.